In semiconductor processing, a semi-conducting wafer must be processed in a multiplicity of fabrication steps, i.e., as many as several hundred, in order to complete the manufacturing of an IC device. These processing steps may include etching, cleaning, deposition and various other processing procedures. A variety of chemicals, including liquids and gases must be used in the various processing steps either to etch a specific feature on the IC chip, to clean after certain processing steps, to deposit layers from reactant chemicals, or to carry out other necessary processing steps.
A variety of specialty chemicals are used for photo and metal cleaning processes. An important requirement for such speciality chemicals, i.e., photoresists, developers, spin-on glass and polyimide is the transporting and storage of the materials. In the case of a photoresist material, the photosensitivity and the lifetime of such a material depends on its storage temperature. It is important to maintain such materials within a specification of 5 to 20.degree. C. for a photoresist/developer and -20 to 10.degree. C. for spin-on glass/polyimide materials.
The transporting of these speciality chemicals, especially liquids, or the delivery from a storage reservoir (i.e., a holding tank) to a processing chamber where the liquid is used is another important aspect of the fabrication process. A process liquid, such as that of a photoresist or a developer, can normally be transported in a fluid passage such as a stainless steel tubing by electrical pump means. One of such conventional liquid delivery system for a photoresist is shown in FIG. 1.
As shown in FIG. 1, the photoresist delivery system 10 generally consists of a liquid reservoir or a holding tank 12, an electrical pump 16, a filter means 18, a needle valve 22, a manual shut-off valve 24 and a drain tank 28. The outlet 32 from the filter means 18 sprays a jet of the photoresist material onto a rotating wafer such that the wafer can be uniformly coated with a thin layer of the photoresist material. The filter means 18 (or a liquid/air separating means) is a device wherein air bubbles trapped in the photoresist solution can be separated from the solution and be released out of the system through needle valve 22. During the process when the photoresist material 14 contained in the holding tank 12 is pumped by the electrical pump 16, air bubbles can be generated and are trapped in the photoresist solution contained in the flow passage 20. When the liquid containing air bubbles passes through the flow passage 20 and enters into the filter means 18, the air bubbles are more likely separated and cumulated to the top of the filter means 18. A jet of the photoresist solution is then released from outlet 32 onto a rotating wafer 26. During normal operations, the needle valve 22 is opened slightly such that the photoresist liquid containing air bubbles can be pushed out of the filter means 18 through passage 30 and needle valve 22 into a waste drain tank 28. The flow of the waste photoresist solution can further be controlled by a manual shut-off valve 24 positioned in between the needle valve 22 and the drain tank 28.
During normal operations, a small amount of air bubbles can be purged out by the above described procedure, i.e, by leaving the needle valve 22 slightly open such that the pressure in the filter means 18 pushes out air bubbles together with a volume of the photoresist solution. However, when a large volume of air bubbles is generated, i.e., during a maintenance procedure of filter replacement or during a photoresist solution change in the holding tank 12, the filter means 18 cannot effectively exhaust the air bubbles unless a large volume of the photoresist solution is purged out and wasted. In other words, the filter means 18 is no longer effective in separating and accumulating the air bubbles when the volume of the bubbles exceeds a critical amount.
When a wafer surface is coated with a photoresist material, the volume of the photoresist material coated and the resulting photoresist film formed must be quantitatively controlled to a high accuracy. Since the presence of air bubbles in the photoresist solution decreases the amount of the photoresist, the amount of the photoresist material available for covering the wafer surface is reduced accordingly. A non-uniform coating and subsequently, a defective pattern can be produced under such circumstances. A poor coating of photoresist film and a poor patterning can result from such a defective coating process due to the presence of air bubbles.
It is therefore an object of the present invention to provide a method of recovering process liquid and eliminating trapped air from such liquid that does not have the drawbacks and shortcomings of the conventional methods.
It is another object of the present invention to provide a method for recovering process liquid and eliminating trapped air in the liquid by utilizing a manual pump to return the process liquid containing trapped air back into a liquid reservoir.
It is a further object of the present invention to provide a closed-loop method for recovering process liquid and eliminating trapped air in the liquid by utilizing a manual pump constructed mainly of a bellow structure.
It is still another object of the present invention to provide a closed-loop method for recovering process liquid and eliminating trapped air in the liquid by utilizing a manual pump that is activated only when excessive amount of trapped air is detected in the closed-loop process liquid flow system.
It is yet another object of the present invention to provide a method for recovering process liquid and eliminating trapped air in the liquid such that a waste of the process liquid can be greatly reduced due to the trapped air problem.
It is another further object of the present invention to provide an apparatus for recovering process liquid and eliminating trapped air in the liquid which consists of a bellow-type manual pump that can be operated when excessive trapped air in the liquid is detected.